Vascular access catheters may be inserted into a patient to permit the infusion of liquid and drugs into the patient's blood supply and for periodic sampling of the patient's blood. A needle-free system may provide a luer or similar connector at the distal end of the catheter to allow a syringe or IV set to be attached to or removed from the catheter as desired.
When the catheter is not connected to an infusion or sampling device, it is important that it can be closed to prevent the introduction of contaminants into or loss of blood out of the catheter. For this purpose, it is known to place a bidirectional valve in series with the luer connector that opens only under predetermined threshold pressures associated with infusion into the patient or sampling of blood from the patient.
A common bidirectional valve of this type provides a dome, for example, fabricated of silicon rubber, having a cross-slit that opens under pressure. The dome provides for different threshold pressures for opening the slit depending on the direction of flow, with flow into the concave side of the dome occurring at a lower pressure than flow into the convex side of the dome. Normally it is desired that the infusion threshold pressure be lower than the aspiration or blood sampling pressure.
When blood is drawn out through such a catheter valve, it is normally desired to flush the valve mechanism with a counter-flow of an infusion liquid such as saline solution. In this respect, it is important that the flushing saline flow occur along substantially the same path as that to which the blood flowed.
A slit dome valve provides a relatively simple mechanism to generate a bidirectional valve opening under different predetermined pressures associated with different flow directions. Nevertheless, fabrication of the slit valve can be problematic. If the slit is not cut perfectly, the resulting valve may leak under low pressure or exhibit significant variations in threshold pressure.